| Continuous cooling deformation is a promising plastic deformation technique,which combines the characteristics of small grain size in low temperature deformation and uniform grain size in high temperature deformation,and is expected to improve the properties of magnesium alloy products.The thermal torsion deformation is non-uniform,and the deformation velocity and strain of the bar sample are closely related to the radius,which can make the same sample provide more experimental data and save the experimental cost.Therefore,the study of the microstructure and mechanical properties after thermal torsional deformation withcontinuous cooling has important guiding significance for practical production.Using Gleeble 3500 thermal simulation testing machine of AZ80 magnesium alloy extrusion state was carried out by different cooling rate（380℃-260℃,380℃-280℃,380℃-300℃and 380℃-320℃）continuous cooling hot torsion deformation and aging,using OM,SEM,hardness testing and EBSD analysis method to study the different cooling rate after hot torsion deformation,center,middle and surface of the same sample of the microstructure and hardness.The evolution of grain size,microstructure and the second phaseβ-Mg17Al12,as well as the relationship between microstructure and mechanical properties were analyzed.The results show that:The sample form gradient formed along the radius after torsional deformation.As the strain increases,the grain size becomes smaller and smaller.With the decrease of the cooling amplitude,the grain size of the three parts showed the trend of decreasing,and the proportion of dynamic recrystalstallization increased with the decrease of the cooling range.The dynamic recrystallization of the 380℃-280℃has the best grain and the best effect.At the same cooling range,as the stress variable and the strain rate increases,and under the same strain,the deformation cooling range decreases.After the thermal torsion deformation of different temperature ranges,the texture dispersion increases.As the strain increases,the non-base component becomes stronger and closer to the（0001）,the angle of（0001）base surface from the bar axis becomes smaller,the center contains[10（?）1]fabric component,the central non-base component becomes weaker and weaker,（0001）becomes stronger,and the edge starts the[2（?）（?）4]component and finally evolves into[10（?）2]component.After the ageing of torsion sample under different deformation conditions,theβ-Mg17Al12 precipitation increases at any time,increasing before decreasing with the decrease of the cooling amplitude.After the deformation of 380℃-280℃.The different stress variables and cooling amplitude change the precipitation mode and precipitation sequence of the β-Mg17Al12phase.After the deformation of the continuous temperature cooling,the hardness value from the center to the surface is increasing,with the ageing time,the hardness increases,and the hardness value from the center to the surface maintains the same rule.With the decrease of cooling range,the hardness value drops first,then rises,then decreases and then rises.When380℃-280℃deformation,the hardness is always higher than other cooling range deformation,and the surface time hardness value of 380℃-280℃can reach 102～104HV. |
